linux-kernel - Re: [PATCH 2/4] rcu: Irq nesting is always 0 on rcu_enter_idle

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Date:	Tue, 29 Nov 2011 02:00:48 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Josh Triplett <josh@...htriplett.org>
Subject: Re: [PATCH 2/4] rcu: Irq nesting is always 0 on rcu_enter_idle_common

On Mon, Nov 28, 2011 at 04:29:14PM -0800, Paul E. McKenney wrote:
> On Mon, Nov 28, 2011 at 10:24:45PM +0100, Frederic Weisbecker wrote:
> > So pass 0 directly as a nesting value on the tracing calls.
> > 
> > Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> > Cc: Josh Triplett <josh@...htriplett.org>
> > ---
> >  kernel/rcutree.c |    5 ++---
> >  1 files changed, 2 insertions(+), 3 deletions(-)
> > 
> > diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> > index c2aaadf..b80cb41 100644
> > --- a/kernel/rcutree.c
> > +++ b/kernel/rcutree.c
> > @@ -350,11 +350,10 @@ static int rcu_implicit_offline_qs(struct rcu_data *rdp)
> >   */
> >  static void rcu_idle_enter_common(struct rcu_dynticks *rdtp)
> >  {
> > -	trace_rcu_dyntick("Start", rdtp->dynticks_nesting);
> > +	trace_rcu_dyntick("Start", 0);
> >  	if (!idle_cpu(smp_processor_id())) {
> >  		WARN_ON_ONCE(1);	/* must be idle task! */
> > -		trace_rcu_dyntick("Error on entry: not idle task",
> > -				   rdtp->dynticks_nesting);
> > +		trace_rcu_dyntick("Error on entry: not idle task", 0);
> >  		ftrace_dump(DUMP_ALL);
> >  	}
> >  	/* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
> 
> Queued, again updating to work around the mid-air collision.
> 
> 							Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
> rcu: Irq nesting is always 0 on rcu_enter_idle_common
> 
> Because tasks don't nest, the ->dyntick_nesting must always be zero upon
> entry to rcu_idle_enter_common().  Therefore, pass "0" rather than the
> counter itself.

And with a better changelog.

Thanks!

> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Josh Triplett <josh@...htriplett.org>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> 
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index 54d9b4f..e0f5072 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -350,12 +350,11 @@ static int rcu_implicit_offline_qs(struct rcu_data *rdp)
>   */
>  static void rcu_idle_enter_common(struct rcu_dynticks *rdtp, long long oldval)
>  {
> -	trace_rcu_dyntick("Start", oldval, rdtp->dynticks_nesting);
> +	trace_rcu_dyntick("Start", oldval, 0);
>  	if (!is_idle_task(current)) {
>  		struct task_struct *idle = idle_task(smp_processor_id());
>  
> -		trace_rcu_dyntick("Error on entry: not idle task",
> -				   oldval, rdtp->dynticks_nesting);
> +		trace_rcu_dyntick("Error on entry: not idle task", oldval, 0);
>  		ftrace_dump(DUMP_ALL);
>  		WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
>  			  current->pid, current->comm,
> 
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